The present invention is directed generally to a method and apparatus for controlling a compressor of the type used in the delivery of pressurized fluid into a pressurized fluid system such as, for example, a vehicle pneumatic suspension system, whereby the delivery of the pressurized fluid into the pressurized fluid system can be cycled on and off to protect the compressor against overload and damage caused by overheating.
Damage to the compressor due to overheating can occur, for example, at the pressure valve as a result of the material becoming brittle, which can lead to leaks. Furthermore, the piston ring can sustain damage, which can lead to destruction of the piston ring and, as a result, seizing of the piston.
DE 196 21 946 C1, which is incorporated herein by reference, discloses a control arrangement for a compressor of the general type under consideration in which an estimated value is determined for the operating temperature of the compressor on the basis of empirical values. If a predesignated temperature threshold is exceeded, the compressor can be turned off automatically.
Furthermore, DE 198 12 234 A1, which is incorporated herein by reference, generally discloses that the heat-transfer conditions in the surroundings of the compressor can be estimated, by means of an appropriate model analysis, for example, and that the compressor can then be controlled as a function of the estimated data.
In such prior art arrangements, the actual temperature conditions at the compressor are not determined; rather, they are merely approximated (only estimated values are used). The result of the uncertainty associated with such estimates is inefficient utilization of the compressor if damage is to be safely avoided. Furthermore, such prior art arrangements necessitate sizing the compressor as a relatively large unit, resulting in greater space requirements and higher costs.
DE 198 10 764 A1 generally discloses switching the compressor from continuous operation to a pulsed mode of operation when a certain temperature limit value is reached. That is, the compressor is cycled on and off rapidly. This results in rapid wear of the compressor. This also results in increased current consumption by the electric motor used to drive the compressor primarily because the starting current of the electric motor is considerably higher than the continuous current.
It is desired to provide an improved method and apparatus for controlling a compressor to protect the compressor against overload and damage caused by overheating which avoids frequent on and off cycles while achieving efficient utilization of the compressor.
Generally speaking, in accordance with the present invention, a method and apparatus for controlling a compressor are provided which overcome disadvantages associated with prior art methods and systems.
According to a preferred embodiment of the present invention, to protect the compressor against overload and damage caused by overheating the compressor is cycled off when the temperature measured at the compressor exceeds a maximum temperature selected based on backpressure caused by the pressurized fluid system. The compressor is then cycled on when it has cooled to a preselected restart temperature.
In an alternative embodiment of the invention, time criteria are superposed on the temperature limits for controlling the activation and deactivation of the compressor.
A temperature sensor can be used to measure the temperature at the compressor. This has the advantage of permitting further improved utilization of the compressor, since the temperature at an appropriate place of the compressor can be determined exactly via a temperature sensor, and temperature estimation, into which relatively large tolerances would have to be built for safety reasons, is avoided. Alternatively, the compressor temperature can be determined by computation based on thermal modeling.
In another embodiment of the invention, both the temperature sensor and thermal modeling are utilized, the signal of the temperature sensor being primarily relied on and thermal modeling being used as backup for determination of the temperature value in the event of defect or malfunction of the temperature sensor. This arrangement provides distinct benefits with regard to operating safety.
In an embodiment of the present invention directed to pressurized fluid systems having discrete modes of operation, discrete temperature limit values can be defined as a function of the modes of operation for controlling the compressor during such modes of operation.
The method and apparatus according to the present invention can be used for any type of compressor control, such as for regulation by means of a pressure regulator or a governor, for compressors that can be decoupled via a mechanical coupling from a drive, such as an internal combustion engine, or even for compressors that can be driven via an electric motor. With an electric motor, the present invention safeguards parts that are susceptible to damage, such as brush rockers and motor windings, against damage caused by overheating.
Accordingly, it is an object of the present invention to provide a method and apparatus for controlling a compressor in a pressurized fluid system to protect the compressor against overload and damage caused by overheating that takes into consideration backpressure caused by the pressurized fluid system.
It is another object of the present invention to provide a method and apparatus for controlling a compressor that takes into consideration actual temperature conditions at the compressor to avoid the large tolerances associated with approximating such temperature conditions that would need to be provided for safety reasons.
It is also an object of the present invention to provide a method and apparatus for controlling a compressor that permit simple and understandable control of the compressor and efficient utilization of the compressor.
It is a further object of the present invention to provide a method and apparatus for controlling a compressor that avoids frequent on and off cycles and the associated damage.
It is still another object of the present invention to provide a method and apparatus for controlling a compressor that permits the compressor to be dimensioned as a compact unit.
It is yet another object of the present invention to provide a method and apparatus for controlling a compressor in pneumatic systems having various modes of operation.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The present invention accordingly comprises the various steps and the relation of one or more of such steps with respect to each of the others, and embodies features of construction, combinations of elements, and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.